62 Royal Institution : — 



ones. That lenticular envelope which surrounds the sun, and which 

 is known to astronomers as the zodiacal light, is probably a crowd 

 of meteors ; and moving as they do in a resisting medium they must 

 continually approach the sun. Falling into it, they would be com- 

 petent to produce the heat observed, and this would constitute a 

 source from which the annual loss of heat would be made good. 

 The sun, according to this hypothesis, would be continually grow- 

 ing larger ; but how much larger ? Were our moon to fall into the 

 sun it would develope an amount of heat sufficient to cover one or 

 two years' loss ; and were our earth to fall into the sun a century's 

 loss would be made good. Still, our moon and our earth, if distributed 

 over the surface of the sun, would utterly vanish from perception. 

 Indeed, the quantity of matter competent to produce the necessary 

 effect would, during the range of history, produce no appreciable 

 augmentation in the sun's magnitude. The augmentation of the sun's 

 attractive force would be more appreciable. However this hypothesis 

 may fare as a representant of what is going on in nature, it cer- 

 tainly shows how a sun might be formed and maintained by the 

 application of known thermo-dynamic principles. 



Our earth moves in its orbit with a velocity of 68,040 miles an 

 hour. Were this motion stopped, an amount of heat would be de- 

 veloped sufficient to raise the temperature of a globe of lead of the 

 same size as the earth 384,000 degrees of the Centigrade thermo- 

 meter. It has been prophesied that " the elements shall melt with 

 fervent heat." The earth's own motion embraces the conditions of 

 fulfilment ; stop that motion, and the greater part, if not the whole, 

 of her mass would be reduced to vapour. If the earth fell into the 

 sun, the amount of heat developed by the shock would be equal to 

 that developed by the combustion of 6435 earths of solid coal. 



There is one other consideration connected with the permanence of 

 our present terrestrial conditions, which is well worthy of our atten- 

 tion. Standing upon one of the London bridges, we observe the cur- 

 rent of the Thames reversed, and the water poured upward twice a day. 

 The water thus moved rubs against the river's bed and sides ; and 

 heat is the consequence of this friction. The heat thus generated 

 is in part radiated into space, and then lost, as far as the earth is 

 concerned. What is it that supplies this incessant loss ? The 

 earth's rotation. Let us look a little more closely at the matter. 

 Imagine the moon fixed, and the earth turning like a wheel from 

 west to east in its diurnal rotation. Suppose a high mountain on 

 the earth's surface; on approaching the moon's meridian that moun- 

 tain is, as it were, laid hold of by the moon, and forms a kind of 

 handle by which the earth is pulled more quickly round. But when 

 the meridian is passed the pull of the moon on the mountain would 

 be in the opposite direction, it now tends to diminish the velocity of 

 rotation as much as it previously augmented it ; and thus the action 

 of all fixed bodies on the earth's surface is neutralized. But sup- 

 pose the mountain to lie always to the east of the moon's meridian, 

 the pull then would be always exerted against the earth's rotation, 

 the velocity of which would be diminished in a degree corresponding 



